ISL6567 Datasheet, PDF (14/26 Pages) Intersil Corporation – Multipurpose Two-Phase Buck PWM Controller with Integrated MOSFET Drivers

ISL6567
DIFFERENTIAL AMPLIFIER’S UNITY GAIN NETWORK
The differential amplifier on the ISL6567 utilizes a typical
resistive network along with active compensating circuitry to
set its unity gain. This resistive network can affect the DC
regulation setpoint in proportion to its relative magnitude
compared to the external output voltage setting resistor
divider. Figure 10 details the internal resistive network. For
minimal impact on the output voltage setting, follow the
guidelines presented in “Setting the Output Voltage” on
page 13.
EXTERNAL REFERENCE OPERATION
The ISL6567 is capable of accepting an external voltage and
using it as a reference for its output regulation. To enable this
mode of operation, the MON pin potential has to be below
3.5V and the reference voltage has to be connected to the
REFTRK pin. The internal or external reference mode of
operation is latched in every time the POR is released or the
ISL6567 is enabled. The highest magnitude external
reference fed to the REFTRK pin that the ISL6567 can follow
is limited to 2.3V. The ISL6567 utilizes a small initial negative
offset (typically about 50mV) in the voltage loop at the
beginning of it soft-start, to counteract any positive offsets
that may have undesirable effects. As this initial offset is
phased out as the reference is ramped up to around 200mV,
in order to avoid an error in the output regulation level, it is
recommended the external reference has an amplitude
(final, DC level) exceeding 300mV.
VCC
ISL6567
I_H
(10µA)
EXTERNAL CIRCUIT
VDIFF
+
MON
-
COMPARATOR
+
V_REF
(300mV) ^-
MON
R_S
R_P
Make note that, in these equations, V_REF refers to the
reference of the MON comparator (300mV).
Intersil recommends the MON threshold is set to be tripped
when the external reference voltage reaches at least 90% of
the final DC value. Since PGOOD and OVP monitoring are
relative to the external reference magnitude, it is important to
understand that the PGOOD and OVP thresholds will move
in proportion to the moving reference (externally soft-started
reference). Thus, the absolute thresholds of PGOOD and
OVP.
ISL6567 POWER-GOOD OPERATION
The open-collector PGOOD output reports on the quality of
the regulated output voltage. Once the ISL6567 is enabled
and the MON pin is above its threshold, PGOOD goes open
circuit when the output enters the power-good window (see
the “Electrical Specifications” table starting on page 5, and
stays open for as long as the output remains within the
specified window. The PGOOD is immediately pulled low if
the ISL6567 is disabled by removal of bias, toggling of the
EN pin, or upon encountering of an overcurrent event;
PGOOD is allowed to report the status of the output as soon
as operation is resumed following any of these events.
V_TARGET
V_OUT
REFTRK
+
To V_{TARGET RS}
R_P
ISL6567
V_REF
EXT CIRCUIT
+
E/A
-
FB
R₁
VDIFF
FIGURE 11. SETTING THE MONITORING THRESHOLD AND
HYSTERESIS
While in external reference (ER) mode, the threshold
sensitive MON pin can be used to control when the ISL6567
starts to monitor the output for PGOOD and OVP protection
purposes. As shown in Figure 11, connect the MON pin to
the voltage to be monitored via a resistor divider. An internal
current source helps set a user-adjustable monitor threshold
hysteresis. Choose resistor values according to desired
hysteresis voltage, V_H, and desired rising threshold, V_T.
R_S
=
V_-----H--
I_H
R_P
=
-^R-----^S-----^â‹---^V----^R----^E----^F--
V_T – V_REF
(EQ. 9)
------^V----^O-----^U----^T-------
V_TARGET
=
--------^R----^P---------
R_P + R_S
+
X1
-
VSEN
RGND
-
+
To V_OUT
FIGURE 12. RATIOMETRIC VOLTAGE TRACKING
The MON pin is used in external-reference configurations,
where the reference is controlled by a circuit external to the
ISL6567. As such, the ISL6567 has no way of ‘knowing’
when the external reference has stabilized to its full value, or
is within a certain percentage of its final value. Thus, the
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FN9243.3
May 28, 2009